//设置根目录font-size,1rem=20px
(function(doc, win) {

    var docEl = doc.documentElement,

        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',

        recalc = function() {

            var clientWidth = docEl.clientWidth;

            if (!clientWidth) return;
            if(clientWidth>=750){
                     docEl.style.fontSize = '20px';
                 }else{
                     docEl.style.fontSize = 10 * (clientWidth / 375) + 'px';
                 }
            /*docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';*/

        };

    if (!doc.addEventListener) return;

    win.addEventListener(resizeEvt, recalc, false);

    doc.addEventListener('DOMContentLoaded', recalc, false);
	
})(document, window);




